ESE's works engine tuner

[Frits Overmars]

Excuse my ignorance but why do many of the 2 stroke cranks I see appear to have a cover on the web? Such as the crank above.

Because it's the cheapo solution. The crankshaft shown in my previous post is from the Honda RS250 production racer. The crank webs are forgings with the material distributed correctly for balancing. But that would leave a clobbered external shape, so a tin cover is pressed around the lot.
The crankshaft below is from the NSR500. That was a works racer; no tins there...

[mr bucketracer]

RGV250 cranks come with the center section welded from the Suzuki factory..............

not case harden there then

[swarfie]

That is exactly right Swarfie. I've seen welds where the crank pins were pressed into the flying webs (B), and in some cases also where they were pressed into the outer webs (A). The Hirth joints that made the Swissauto crank so expensive, were not welded.
Attachment 313745

Thanks Frits....I only welded my crank at A in your diagram (only a twin cylinder engine), as I had had a crank years ago turn/move (and subsequently go out of true on the output shaft) that I had made out of two TT500 Yamaha cranks for a mates Matchless twin. I use a "Hurth" coupling of my own design which will never rotate, which is basically square holes in the centre two crank webs with a centre mainshaft with corresponding squares each side of the round centre bearing shaft. This is pressed up with only 0.02mm interference but by it's very nature can never rotate (and has never separated/moved). I'm reminded of the old saying "keep it simple stupid Interesting that I use the original Yamaha TT crankpins (on a 34 mm diameter pin) which even at an interference of the original Yamaha spec at 0.1 mm can still move/slip and is the reason I welded as a precaution more than anything else. So actually IMHO even good design can sometimes (and in the case of a sidecar where the loads are so much more than a solo) come back and bite you in the arse.
As a side note, my "Matchless" replica engine has won the Classic sidecar trophy in NZ 17 times to date and at first attempt in Australia in 2000 took out the Ausy Championship (knocking more than 2 seconds off the classic lap record at Syney's Eastern Creak circuit in the process)....so we'll have no more of this "bad design" BS please from Mr J Quest....sour grapes...not much

[husaberg]

Because it's the cheapo solution. The crankshaft shown in my previous post is from the Honda RS250 production racer. The crank webs are forgings with the material distributed correctly for balancing. But that would leave a clobbered external shape, so a tin cover is pressed around the lot.
The crankshaft below is from the NSR500. That was a works racer; no tins there...

I also note the hand finishing on the rods.

Thanks Frits....I only welded my crank at A in your diagram (only a twin cylinder engine), as I had had a crank years ago turn/move (and subsequently go out of true on the output shaft) that I had made out of two TT500 Yamaha cranks for a mates Matchless twin. I use a "Hurth" coupling of my own design which will never rotate, which is basically square holes in the centre two crank webs with a centre mainshaft with corresponding squares each side of the round centre bearing shaft. This is pressed up with only 0.02mm interference but by it's very nature can never rotate (and has never separated/moved). I'm reminded of the old saying "keep it simple stupid Interesting that I use the original Yamaha TT crankpins (on a 34 mm diameter pin) which even at an interference of the original Yamaha spec at 0.1 mm can still move/slip and is the reason I welded as a precaution more than anything else. So actually IMHO even good design can sometimes (and in the case of a sidecar where the loads are so much more than a solo) come back and bite you in the arse.
As a side note, my "Matchless" replica engine has won the Classic sidecar trophy in NZ 17 times to date and at first attempt in Australia in 2000 took out the Ausy Championship (knocking more than 2 seconds off the classic lap record at Syney's Eastern Creak circuit in the process)....so we'll have no more of this "bad design" BS please from Mr J Quest....sour grapes...not much

So the Matchless is it still three bearing plain center or roller?

[swarfie]

Three roller bearing crank. Parallel roller in the centre and shouldered roller bearings each side for axial alignment. In fact the only bushes left in the engine are in the OHV rockers, even the cams and timing gears run on needle roller bearings. Done it all proper like....unlike the poms

Also made my own rods after a Yamaha one broke in 2010 and wrecked things a bit. The engine makes really good torque and doesn't need to rev past 6500 but the TT rods couldn't hack the pace so made the new ones out of Assab 718. Doubt I'll have to see them for a while.

[Tim Ey]

Talking cranks a question occured to me:
with which size of press fit are Aluminium and tungsten inserts pressed in the crank?

[swarfie]

I don't know as I haven't had to use them to get a balance factor but as there's no load on them they probably only need to be 0.01/0.02 mm press to hold them in place. I work with fits and tolerances on a daily basis for my job (toolmaker) and for like materials a size for size fit is a press fit so only having to allow for a differential in expansion would keep inserts in place.

[Flettner]

I don't know as I haven't had to use them to get a balance factor but as there's no load on them they probably only need to be 0.01/0.02 mm press to hold them in place. I work with fits and tolerances on a daily basis for my job (toolmaker) and for like materials a size for size fit is a press fit so only having to allow for a differential in expansion would keep inserts in place.

Neville M , I assume?

[swarfie]

Neville M , I assume?

You might be able to answer Tim Ey on the subject of crank stuffing plugs better than me Neil.

[Flettner]

You might be able to answer Tim Ey on the subject of crank stuffing plugs better than me Neil.

Yes, I've stuffed a few cranks in my time

[41juergen]

Thank's a lot Wob for the answer about the reeds, will follow that and will do some testing.

Just an other question, does somebody can tell me if the Yamaha stated 87 HP of the mid 90th TZ250 V twins was rear wheel HP or "at the crank"?

Juergen

[husaberg]

Thank's a lot Wob for the answer about the reeds, will follow that and will do some testing.

Just an other question, does somebody can tell me if the Yamaha stated 87 HP of the mid 90th TZ250 V twins was rear wheel HP or "at the crank"?

Juergen

Hello Juergen
Like all Japanese factory hp claims it was measured at the piston ring..............
Unfortunately due to there small size and poor sense of direction, Maybe only 73 or so of those horses where able to find there way back to the rear wheel.

[41juergen]

Thank's Husa, just hoped that they did same like for the road bikes. I'm looking to push my TZR250R (the last 2 stroke for road use what Yamaha produced) to higher limits. Unfortunately it has the same worse bore / stroke ratio like the TZ's at that time (as a lot of the engine parts are exactly the same). But with all the advise from Wob and Frits my sim show up more than 80 HP on the wheel so lets see, next topic is the weld up the ex port and the spigot to finally match the correct dimensions, will report back.
Juergen

[Bert]

Hello Juergen
Like all Japanese factory hp claims it was measured at the piston ring..............
Unfortunately due to there small size and poor sense of direction, Maybe only 73 or so of those horses where able to find there way back to the rear wheel.

Thank's Husa, just hoped that they did same like for the road bikes. I'm looking to push my TZR250R (the last 2 stroke for road use what Yamaha produced) to higher limits. Unfortunately it has the same worse bore / stroke ratio like the TZ's at that time (as a lot of the engine parts are exactly the same). But with all the advise from Wob and Frits my sim show up more than 80 HP on the wheel so lets see, next topic is the weld up the ex port and the spigot to finally match the correct dimensions, will report back.
Juergen

It will be interesting to see where you get too Juergen.
I'd love to see 80+ from my TZ250 (not TZR); while I have a few spare TZ barrels, much rather tinker (likely destroy) some of the 3xv sp barrels (given they are not rocking horse shit).
While you say the parts are exactly the same - there is a number of differences in the port layout and time areas.

[cotswold]

http://www.morebikes.co.uk/scoop-hon...okes-are-back/


Must have seen your work TZee